The present invention relates to a workpiece clamping fixture for rotational machining, having an end face driver for torque transmission from the spindle of a machine tool to the workpiece, the diameter thereof being larger than its length, and the end opposite the work clamping fixture being supported by a centre.
End face drivers of known design are commonly shaped as drive rings which are centrically clamped in a standard three-jaw chuck. They are provided on their circumference with three sharp-edged driving pieces against which the disk-type workpiece is pressed by the action of the opposite centre. Centrical location is achieved from the opposite centre while the driving pieces, the edges of which must be in a plane perpendicular to the axis of rotation, take care of the true position of the workpiece, and of torque transmission against the forces produced in the machining process. It is found to be of a disadvantage, however, that the end face of the workpiece cannot be premachined, because the three driving pieces leave an otherwise too deep an impression on the finished surface. Finishing must be done by a second clamping in a standard three-jaw chuck which method is relatively uneconomical.
It is normal practice that workpiece components of a length very much greater than their diameter, are clamped between two centres, and that at one end face a face driver is applied. Thereby a type of face driver has been introduced comprising a multitude of drive pins, all of which are braced against a common hydraulic cushion. This has the effect of exerting approximately the same pressure on practically all the driving pins, no matter what the true position is of the end face of the workpiece against which they are resting. Balancing is effected by the hydraulic cushion. However, any such hydraulic end face drivers cannot be used in the machining of components, where the diameter is equal, or even greater, than their length. In such cases the component might easily assume an oblique position with respect to its axis, because of the small distance between the two centres, thus executing a wobble in its rotational motion, and making it impossible to be normally machined.
It is the object of the present invention to have a workpiece clamping fixture of the aforementioned type so designed, that even hydraulic end face drivers can be used for the clamping of components, where the diameter might be equal, or even greater, than their length.